This invention relates to systems for measuring and communicating various operating parameters associated with electrical power conductors; more specifically, the invention relates to systems which include line-mounted sensor modules having means for both transmitting signals commensurate with parameter values and optionally for receiving signals to permit time-synchronized data sampling and transmission in a manner allowing highly accurate measurement and analysis of data from a large number of modules at a single ground station.
Various power line mounted apparatus for sensing operating parameters of an associated conductor have been disclosed in the prior art. See, for example, U.S. Pat. Nos. 3,428,896, 3,633,191, 4,158,810 and 4,261,818, as well as the improved systems disclosed in the co-pending applications referenced herein. In general, such systems include line-mounted sensor modules which measure certain quantities associated with operation of overhead power lines, namely, current, conductor temperature and ambient temperature, and transmit such data via a radio link to a nearby ground station. Data from several ground stations is then transmitted to a central control station where it is processed and used to assist in control of the power supplied to the various transmission lines in accordance with the measured parameters.
Prior art systems of this type, while representing a significant improvement over traditional means of measurement and control of power line operating parameters, still have a number of inherent limitations and diadvantages, some of which are addressed in copending application Ser. No. 859,496 of the present inventor, filed concurrently herewith. Said application, for example, provides means for simultaneously measuring current, voltage and phase angle on multiple conductors of a single circuit or of many circuits thereby permitting monitoring of an entire substation. It is possible, however, that the accuracy of measurement of quantities such as voltage on a particular circuit may be adversely affected by adjacent, energized circuits. Also, time synchronized data collection for sequence-of-events application is not possible. Other drawbacks of the previously disclosed systems are high speed sampling for relaying and harmonic measurements is not possible for an entire substation installation; and, the use of certain sensor modules on distribution circuits with relatively small conductor clearances, as compared to extra high voltage transmission circuits, is difficult if not prohibitive.
The objects of the present invention are addressed to providing improvements in power line parameter monitoring and analysis systems which deal with each of the aforementioned disadvantages of prior art systems. Among the specific objects of the invention, all within the context of systems for collecting and transmitting parameters associated with electrical power line operation which employ line-mounted sensor modules, are: to improve the accuracy of voltage measurement in the presence of adjacent conductors, irrespective of whether the latter are energized; to reduce the number of frequency channels required for use by a large number of sensor modules at a substation, thus reducing licensing constraints; to provide hot-stick mountable, integrated sensor modules which can be installed on power lines with relatively close spacing between adjacent conductors; to permit time-synchronized data acquisition from multiple modules within a substation for accurate post-fault, sequence-of-events analysis; to provide means for high speed sampling and comparison of cyclically variable parameters for relaying and harmonic measurement applications; and, to provide communications links other than RF broadcast signals for transmitting data from sensor modules.